This invention relates to solenoid valves for controlling fluid flow and more particularly to an improved form of four-way solenoid valve which combines direct solenoid operation with a pilot operated valve.
There are many varieties of solenoid valves designed for four-way valve operation which might be typically used to operate double acting cylinders and similar devices. Certain of these valves fall into a category known as midget valves, which valves are extremely small and utilized where space and weight considerations are significant and where fairly light loads are encountered. Since both air and liquid applications are typical, it is necessary to accommodate both inlet and exhaust flows and suitable piping is conventionally employed for the purpose. Further, although the valves are primarily designed for the light service application, variations thereof in larger and sturdier enclosures are commonly included for general purpose applications.
One particular form of prior art valve in this category utilizes a body of forged brass which includes a pressure port, a pair of cylinder ports and an exhaust port and requires that a further exhaust port be established through the solenoid valve assembly. In this prior art design a pilot valve is piston-operated, causing axial movement of a valve disc between normally open and closed positions. The direct operated valve portion is configured as a double-ended solenoid plunger which carries spring-loaded valving elements at each end for cooperation with one valve seat in the body and the other in the pole piece of the solenoid assembly. A separate exhaust passage is formed through the pole piece and typically plumbing is required at this location for routing the exhaust flow.
In this prior art design the piston-operated valve is provided with sufficient radial disc clearance to allow adequate flow to and from a cylinder port, but this tends to provide poor guidance for the piston-operated valve disc. Accordingly, the disc is not assured of repetitive seating onthe same impression in its resilient surface. Further, since lateral passages are provided in the body casting at this location, any eccentric positioning of the pilot valve disc may create partial blockages and a restriction for the flow of fluid.
The requirement for a second exhaust port in this prior art design necessitates the stocking of specialized solenoid valve parts in addition to standard solenoid parts which are typically used in many varieties of valves. Further, additional piping or muffling may be required in this design because of the second exhaust port. Finally, this type of design tends to place limitations on the exhaust orifice size and pressure rating which may produce compromises for the electromagnetic valve operator.